1. Field of the Invention
The present invention relates to a magnetic recording device that includes a magnetic storage medium that stores therein servo information, a magnetic recording medium, and a servo information recording method.
2. Description of the Related Art
To cope-up with the requirement of increasing the recording capacity of a computer, recently there has been a trend to increase the storage capacity of a magnetic recording device such as a hard disk drive (HDD) used in the computer. Higher storage capacity can be achieved by increasing the recording density of a magnetic recording device. To increasing the recording density, one approach is to reduce the size of the recording magnetic domain on a magnetic recording layer generated by a signal magnetic field using a magnetic head. As a recording method of this type, there is conventionally known the perpendicular magnetic recording (PMR).
The PMR is a method of recording information by magnetizing a magnetic material in a direction perpendicular to a recording surface of the recording layer of the magnetic recording medium. In the PMR, however, if information is recorded at ultra-high density equal to or higher than 100 Gbit/in2, side fringes on side edges of a magnetic head, which records information on the magnetic recording medium, cause the magnetic head to wrongly perform a write operation on a track adjacent to the target track, resulting in a recording defect and a reproducing defect.
To take care of this issue, there has been proposed the discrete track recording (DTR) based on the PMR. In the DTR, magnetic regions and nonmagnetic regions are alternately formed on the recording layer in the direction perpendicular to the direction of radius of the magnetic recording medium. The magnetic regions are formed with a magnetic material, and data is recorded in the magnetic regions. The nonmagnetic regions are formed with a nonmagnetic material, and no data is recorded in the nonmagnetic regions. A nonmagnetic region is sandwiched between adjacent tracks. The DTR prevents data from being erroneously written on a track adjacent to the target track, and realize good recording and reproducing characteristics.
Meanwhile, there have been proposed a magnetic recording device that employs a composite head that includes two heads. The composite head includes a recording head and a reproduction head. A thin-film inductive head is employed as the recording head for writing data on the magnetic recording medium. A magnetoresistive head (MR head) is employed as the reproduction head for reading the data from the magnetic recording medium. In a magnetic recording device having a rotary drive structure, the composite head is supported on a tip end of a head actuator, and the composite head is controlled to be moved in a diameter direction of the composite head, i.e., a direction of traversing tracks of the magnetic recording medium so as to be positioned in a desired sector. A data region including the magnetic recording regions and the nonmagnetic regions, and a servo region are provided on the recording surface of the magnetic recording medium. In the servo region, position information such as track positions and sector positions is recorded at predetermined intervals in a track direction.
The data region of the magnetic recording medium includes first area and second areas. A surface of each of the first area is effective as a magnetic recording region. On the other hand, a surface of each of the second area is ineffective as a magnetic recording region. Each of the first area is convex, has a magnetic film on its surface, and serves as the magnetic region for recording information. Each of the second area is concave and serves as the nonmagnetic region in which no information is recorded. Namely, the second areas are constituted as the nonmagnetic regions because of their concave shape, although sometimes a magnetic film is formed on the surface of the second areas.
To record and reproduce information with high precision on and from a track of the data region of such a recording medium that can realize high-density recording, it is necessary to position the head on the track of the data region at high precision. This means that it is necessary to record servo information in the servo region at high precision. With the conventional technique, the servo information is recorded in the servo region using a servo information recording apparatus. Similarly to the data region, if the servo information is recorded at high precision and high density, side fringes are disadvantageously generated. As a result, it has become difficult to further narrow the pattern width.
As a conventional technique for recording the servo information at high precision, there is known a servo information recording technique as disclosed in JP-A H7-65363 (KOKAI). In this technique, an information region for follow-up control over the mask pattern (hereinafter, “follow-up control information region”) is formed in the servo region that includes the magnetic film formed on a substrate. In the follow-up control information region, pits serving as the nonmagnetic regions are arranged in a direction of a track width of the data region. The servo information is recorded in a region between the adjacent pits. Due to such a structure, the influence of the side fringes can be lessened.
In the conventional technique, the mask pattern of the follow-up control information region is formed by, for example, irradiating a laser beam onto a base material, on which a photoresist is applied, to cut off the pattern into tracks using a cutting machine. Due to this, the tracks on the mask pattern depend on the properties of the cutting machine. To magnetically record the servo information into the mask pattern, it is necessary to appropriately position a recording head on the mask pattern while following up the form of tracks each formed by the cutting machine.
With the conventional technique, therefore, if tracks of the servo region are eccentrically fixed, it is necessary to employ a dedicated servo information recording apparatus that includes a fine-movement actuator such as a piezoelectric element that causes the recording head to make a fine movement so as to follow up the mask pattern.
If each track formed into the mask pattern by the cutting machine is in the form of a true circle, it is easy to move the recording head to follow up the mask pattern using the fine-movement actuator. However, if vibrations occur during cutting the pattern into the tracks using the laser beam, tracks with irregular shapes are formed. With the tracks having irregular shapes, it is difficult to move the recording head to follow up the mask pattern.
Furthermore, if the servo information is to be recorded on one recording medium, the servo information recording apparatus becomes busy for a long time. Moreover, if the recording density is high, the number of tracks considerably increases so that it takes still longer time to record the servo information using the servo information recording apparatus. To reduce processing time for manufacturing process of the recording medium, it is disadvantageously necessary to provide a plurality of servo information recording apparatuses.
Moreover, if a track pitch of the recording medium is narrower, the mask pattern is smaller. If so, higher positioning precision is required for positioning the recording head on the mask pattern using the servo information recording apparatus. This makes it further difficult to realize the servo information recording apparatus.
In this manner, with the servo information recording technique for the conventional magnetic recording medium, a plurality of dedicated or high-precision servo information recording apparatuses are often required to record the servo information with high precision.